We wish to pursue our characterization of the newly discovered XLR (X-chromosomal, lymphocyte regulated) gene family with respect to its pattern of expression in B and T cells, the number of active genes, their chromosomal organization and the location of the protein products in the cell. These data should provide important clues as to the function(s) of this family of sequences and would help to determine the course of future experimentation. Other experiments to determine the function of XLR gene products involve introducing XLR carrying vectors into B cell tumors at various stages of differentiation to determine the influence of either positive (sense-strand) or negative (anti-sense strand) expression. Alternatively, we may try protein or anti-XLR antibody injection via red cell ghosts. In addition, we will try to determine the structural linkage between this locus and the xid defect of the CBA/N mouse by restriction fragment length polymorphism analysis (RFLP's) and the introduction of portions of the XLR locus into mouse embryos carrying the xid defect. These and alternative strategies should be helpful in determining the precise defect in XLR which causes the xid phenotype. Understanding the molecular basis of the xid mutation may provide insights into the nature of the late stage B cell differentiation and the postulated two subsets thought to constitute the immunoglobulin producing response. We will also sequence and develop antisera against the recently isolated human equivalent of XLR and determine whether any of the inherited X-linked immunodeficiency disorders appears to be aberrant in this gene family. Any such linkage between XLR and these defects would provide the first structural basis for a human X-linked immunodeficiency as well as important additional clues as to the genetics of this locus.